Here's the minimum required services to load Windows(XP Pro) and get online via a broadband connection with a static ip address:

Plug and Play (Automatic)
Remote Procedure Call (RPC) (Automatic, vital for operation and can't be disabled anyway)
DNS Client (Automatic)
Network Connections (Manual)

For a connection with a dynamic IP address you need to keep DHCP Services set to Automatic.

For dialup, you need all of the previously mentioned, DHCP Services, and Telephony set to Automatic.

If you're wondering where your sound went, set Windows Audio to Automatic... as it manages your sound through an additional software layer(thanks a lot Microsoft).

In keeping only the services I mentioned enabled, I've been able to reduce my ram usage to less than 50MB for Windows(this is including Explorer.exe), which definitely gives your applications some room to play around with.


One last note: You need Cryptographic services enabled to install most Microsoft products(namely DirectX and Windows Media Player). I recommend keeping it set to manual. This way, the installation will call it when it needs it, while the rest of the time it's disabled.